Heat exchanger and use thereof in showers

ABSTRACT

An improved heat exchanger design is disclosed. The design of the heat exchanger provides for a safe separation of the flow streams even in the event of leakage. An improved heat recovery device for use in the drain conduit of standard shower installations, comprising the heat exchanger of the invention, is also disclosed.

RELATED APPLICATIONS

This application claims priority from U.S. Provisional Patent Application Ser. No. 60/815,773, filed Jun. 22, 2006, which is hereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

This invention relates generally to the field of heat exchangers, and more particularly to a heat exchanger for use in a personal shower environment which recaptures heat from waste water passing through the shower drain and distributes that heat into the cold water entering the shower to raise the temperature of the cold water and thus reduce the amount of hot water required to maintain a given shower temperature.

BACKGROUND OF THE INVENTION

This invention relates generally to the field of heat exchangers, and more particularly to a heat exchanger for use in a shower environment which recaptures heat from waste water passing through the shower drain and distributes that heat into the cold water entering the shower to raise the temperature of the cold water and thus reduce the amount of hot water required to maintain a given shower temperature.

It is well known that showering for the purpose of maintaining cleanliness is almost universally practiced in civilized society. There is hardly any form of habitation, whether personal residences, commercial habitations, or miscellaneous bathing facilities, that does not provide the necessary equipment for showering. Showering has become, in modern society, so commonplace that many individuals shower at least once per day. Many prefer showering to bathing because it is ready for use more quickly, cleans more effectively, and may require less hot water if not excessive in duration.

Despite the fact that showers of reasonable length and temperature may consume less hot water than bathing in a tub, the fact remains that a substantial amount of hot water is lost down the drain, since the shower water remains in the shower installation for only a very brief period of time, in which only a small portion of it's heat energy is utilized. This, of course, is wasted energy, and represents an expense in fuel or electricity to heat the water which could be substantially reduced if some of the unused heat in the waste water could be recaptured and put to use.

Devices for efficiently and economically exchanging heat between two fluids have been well known for many years and are widely used throughout industry. None of these devices, however, would be practical or effective in the application of recovering heat from the waste water passing through the drain conduit of a shower installation because of the unique environment and requirements of such a system, such as not interfering with the free flow of drain water, not being conducive to clogging, being easy to clear in the event of a clog using standard methods, adapting to existing standard plumbing fittings, and fitting into the typically available space. Additionally, this device must meet the applicable plumbing standards & codes in order for it to be legally and widely installed. Further, this device must have an adequate heat recovery efficiency to justify its purchase & installation cost to the consumer. U.S. Pat. No. 5,791,401 discloses a heat recovery device for personal showers, however the designs disclosed therein are expensive to manufacture because of the complex assembly process, and the inefficient use of materials, and the device has a low operating efficiency.

Thus, there is a need for a more practical, less expensive, more efficient, maintenance-free, and trouble-free device for recapturing heat from shower waste water after it has entered the shower drain and transferring it to the incoming cold water before the cold water is mixed with the hot water and enters the shower head.

BRIEF SUMMARY OF THE INVENTION

The present invention substantially if not entirely meets all of the previously mentioned requirements for a heat recovery device intended for use in the environment of personal shower installations.

Thus, in its broader aspects, the present invention is a heat recovery device adapted for use in the drain conduit of standard shower installations having a hot water supply line, a cold water supply line, a means for mixing water from both lines to deliver water at a suitable temperature to the shower head, and a drain conduit for disposing of waste water passing out of the shower installation, the heat recovery device transferring heat from the waste water to the cold water in the cold water supply line. In this environment, the heat recovery device of the present invention comprises a generally tubular first conduit formed of a material having a high degree of thermal conductivity, this conduit having an inlet that is connected to and in close proximity to the shower drain so that waste water entering the drain will pass into the conduit inlet end, and the exit end of the first conduit connected to the waste water plumbing to receive the water exiting the first conduit. A second conduit means is connected in series with the cold water supply line and is thermally operatively associated with the first conduit in such a way as to transfer the thermal energy from the warm drain water passing through the first conduit to the cold supply water passing through the second conduit and thus raising the temperature of the cold supply water before it reaches the mixing means.

In a more limited aspect, the area between the inlet and outlet ends of the first conduit are disposed at a lower level than the ends, so that conduit remains substantially filled with water at all times and functions as a water trap. Preferably, the central portion of the first conduit lies in a plane that is disposed at an angle to the vertical plane that the inlet and outlet ends of the first conduit lie in, and most preferably, the central area of the first conduit lies in a substantially horizontal plane.

The heat recovery device comprises a second conduit formed of a material having a relatively high degree of thermal conductivity, and being disposed in an intimate heat exchange relationship with the first conduit, and having an inlet end connected to the upstream portion of the cold water supply line, and a downstream portion connected to the mixing valve, so that cold water passing through the second conduit receives thermal energy from the warm waste water passing through the first conduit.

In certain embodiments, the first conduit is formed with helical convolutions in the outer surface, such that the external surface of these convolutions, when combined with a surrounding smooth tubular member, will form the second conduit means, thus placing the two conduit means in intimate thermal contact with each other. The convolutions in the wall of the first conduit also serve to impart turbulence to the drain water passing therethrough, thus increasing the convective heat transfer from the drain water to the wall of the conduit. The convolutions in the wall of the first conduit also serve to impart a spiraling flow to the drain water passing through, thus increasing the velocity of the flow and therefore increasing the rate of convective heat transfer from the drain water to the wall of the conduit.

In one variation of this embodiment, the spiral convolutions are comprised of a single helical groove.

In another variation of this embodiment, the spiral convolutions are comprised of two or more helical grooves, which are joined near the ends by a partial or complete circular groove in said first conduit. These circular groove features allow the multiple spiral flow paths of the second conduit to be in communication with each other, and thus allow the cold water to flow through all of them in parallel.

In another variation of this embodiment, the multiple spiral convolutions are comprised of two or more helical grooves, but rather than being joined by a circular feature near the ends of the first conduit member, they are joined by circular features near the ends of the outer tubular member. These features allow the multiple spiral flow paths to be in communication with each other, and thus allow the cold water to flow through them in parallel. Having this feature on the outer tubular member, instead of the first (inner) conduit member, has the benefit of removing the interruption to the inner helical flow path that this feature creates in the first conduit. Therefore, the inner helical flow will be more robust with this configuration, and have improved convective efficiency.

In another variation of this embodiment, the spiral convolutions are asymmetrical in cross section, such that the flow in the first conduit will encounter steeper oblique obstructions along the outer walls as it goes forward through the conduit, thus imparting more rotational energy to the flow stream, and more effectively increasing the velocity of the flow and convective efficiency. The asymmetry of the helical feature provides a smooth transition on the downstream side of the feature, thus encouraging the flow to remain attached to the surface, and causing the next steep oblique surface to be more effective in promoting the helical flow pattern favoring convective efficiency.

I another variation of this embodiment, the outer wall of the first conduit is made up of two layers of material. This feature allows the second conduit to use the outer layer of the first conduit as its functional inner surface, so that the first and second conduit do not share a common wall. This is an important and required safety feature (for example in U.S. plumbing installations carrying drinking water), which is designed to prevent a leak in any one conduit wall from flowing into the other conduit. Preferably, a narrow gap is present between the two layers of the first conduit wall, so that a leak from either conduit mean will have a path to the outside and therefore be detectable. For example, to ensure formation of said narrow gap during the manufacturing process, a fibrous material that can withstand the high temperatures and stresses of the manufacturing processes may be placed between the two layers of the first conduit wall prior to the forming process, so that a leak from either conduit mean will have a path to the outside and therefore be detectable.

In one embodiment of this invention, the single, helically convoluted first conduit which extends substantially in the horizontal plane and has ends that bend upward at approximately 90 degrees to the vertical plane, combined with the relatively smooth outer tube over the convoluted area forming the second conduit means, is substantially straight.

In another embodiment, the convoluted, horizontally positioned part of the first conduit means is curved approximately 180 or more degrees while remaining in the substantially horizontal plane, thus locating the ends relatively close to each other, more closely representing the configuration of a conventional drain trap. An exemplary drawing of this embodiment is shown in FIG. 9.

In another embodiment, two separate sections of the first conduit are joined with an approximately 180-degree conduit section, thus disposing the two sections in a substantially parallel position to each other. The two respective second conduits are connected by a connector conduit that provides for a flow path from one second conduit means to the other.

In yet another embodiment, three, four or more sections of the first conduit are joined with suitably angled conduit sections, elbows or fittings, and the corresponding second conduit sections are brought in fluid communication by two, three or more connector conduits.

Having briefly described the general nature of the present invention, it is a principle object thereof to provide a heat recovery device adapted for use in the drain conduit of a shower installation in which heat in waste water passing through a shower drain conduit is recaptured by transferring it to the cold supply water before it enters the mixing valve and is combined with the hot water supply and enters the shower head.

Another object of this invention is to provide a heat recovery device as disclosed which is designed and constructed to replace the standard drain trap present in all shower equipment installations and to function in the same manner as a water trap.

It is another primary object of the present invention to provide a heat recovery device as disclosed which can be easily and economically manufactured and installed in new or existing shower equipment installations and is entirely compatible with industry standard plumbing equipment utilized in such installations.

It is still another object of the present invention to provide a heat recovery device which is situated in a shower equipment installation such that it is in close enough proximity to both the shower drain and the mixing valve so as to minimize the heat lost in the existing conduits.

It is still another object of the present invention to provide a heat recovery device that provides an intimate thermal contact between the drain water of a shower installation and the cold supply water of a shower installation, such that a substantial proportion of the thermal energy in the waste water is recovered by transferring the energy to the cold supply water.

It is still another object of the present invention to provide a heat recovery device that provides a safe separation between the drain water of a shower installation and the cold supply water of a shower installation, such that a failure of either conduit means will not allow contamination from the water in either conduit to enter the other conduit. It is still another object of this invention to provide a heat recovery device that requires a minimum amount of material & labor to manufacture in order to be cost effective relative to the value of the heat energy that it can recover.

It is another object of this invention to provide a design that uses the most highly automated & accurately repeatable manufacturing processes that can be economically employed to produce the product.

It is another objective of this invention to provide a design that has the highest possible efficiency for its size and for the amount of material used in its construction.

The present invention includes a heat recovery device adapted for use in the drain conduit of a shower installation having a hot water supply line, a cold water supply line, a means for mixing water from both said lines to deliver water at a suitable temperature to a shower head, and a drain conduit for disposing of waste water passing out of the shower installation, the heat recovery device transferring heat from the waste water to the cold water supply before it enters said mixing means, said heat recovery device comprising a section of generally tubular first conduit formed of a material having a relatively high degree of heat conductivity, said first conduit having an inlet end connected to an upstream portion of said drain conduit and an outlet end connected to a downstream portion of said drain conduit so that waste water passing through said drain conduit also passes through said first conduit, said inlet and outlet ends of said first conduit being connected to said upstream and downstream portions respectively of said drain conduit in such a manner that said first conduit between said inlet and outlet ends is disposed at a lower level than said inlet and outlet ends so that said first conduit remains filled with water at all times and functions as a water trap, and contains at least one helical convolution formed in the wall of said first conduit, said heat recovery device further comprising conduit means connected into said cold water line of said shower equipment and being thermally operatively associated with said first conduit such that cold water passes through said conduit means while passing through said cold water line to be exposed to heat from said first conduit from waste water passing therethrough, said conduit means comprising a second conduit formed of a material having a relatively high degree of heat conductivity, said second conduit being disposed in intimate heat exchange relationship with said first conduit, said second conduit having an inlet end connected to an upstream portion of said cold water line and an outlet end connected to a downstream portion of said cold water line so that cold water passing through said cold water line also passed through said second conduit and receives heat transferred to said first conduit from said waste water, said second conduit having an inner wall that comprises a layer of thermally conductive material that conforms generally to the said helically convoluted outer surface of said first conduit, said second conduit having an outer wall consisting of a substantially tubular member that fits closely to the largest diameter parts of said convoluted inner wall and is suitably joined to it, so that the second conduit is comprised of the helical lumen formed between said outer and said inner walls, said outer wall containing at least one opening at each end of the helical lumen for inlet and exit flow respectively of said cold water supply suitable for adapting to common plumbing fittings, whereby heat from said waste water is conducted through said first conduit means to pre-heat cold water passing through said second conduit means before reaching said mixing means.

In variation of this embodiment, said first conduit means of said heat recovery device is substantially straight and generally horizontal, said inlet and said outlet ends are disposed at substantially 90 degrees to said first conduit means, and disposed substantially vertically.

In a further variation of this embodiment, two assemblies of said first conduits and said conduit means are connected in series using a 180 degree conduit section to join them, and are arranged substantially parallel to each other in the generally horizontal plane, and said inlet end of the upstream section and the exit ends of the downstream section of the first conduit sections are disposed in a substantially vertical plane, so that they are parallel to each other and in close proximity to each other.

In yet a further variation of this embodiment, said first conduit forms a loop in the generally horizontal plane, or at a small angle to the horizontal plane, said inlet and outlet ends disposed in relative close proximity to each other, said inlet and said outlet ends disposed at substantially 90 degrees to said first conduit means, said inlet and outlet ends disposed substantially vertically.

In certain embodiments, a spacer material is located between the outer surface of the first conduit and the outer surface of the inner wall of the second conduit. In other embodiments, the outer surface of the first conduit and/or the outer surface of the inner wall of the second conduit is grooved or textured. The spacer material may be, for example, high temperature fibrous material, metal mesh, metal wire, glass fibers, carbon fibers, aramid fibers, or ceramic fibers.

The present invention also includes heat exchanger for transferring heat between a first liquid and a second liquid, comprising a section of generally tubular first conduit for conducting a first liquid, having at least one helical convolution formed in its wall; and a second conduit being thermally operatively associated with said first conduit, said second conduit being disposed in intimate heat exchange relationship with said first conduit, said second conduit having a convoluted inner wall that comprises a layer of thermally conductive material that conforms generally to the outer surface of said helically convoluted first conduit, said second conduit having an outer wall consisting of a substantially tubular member that fits closely to the largest diameter parts of said convoluted inner wall and is suitably joined to it, so that the second conduit is comprised of the helical lumen formed between said outer and said inner walls, said outer wall containing at least one opening at each end of the helical lumen for inlet and exit flow of the second liquid, respectively.

In some embodiments, the heat exchanger of the invention further comprises a spacer material, which is located between the outer surface of the first conduit and the outer surface of the inner wall of the second conduit. In certain embodiments, the spacer material may be metal mesh, metal wire, glass fibers, carbon fibers, aramid fibers, or ceramic fibers. In other embodiments, the outer surface of the first conduit and/or the outer surface of the inner wall of the second conduit is grooved or textured. In these and other embodiments, a space is located between the outer surface of the wall of the first conduit and the outer surface of the inner wall of the second conduit, said space being in gaseous or liquid communication with the surrounding environment, and said space providing a means for accidental leakage of the first or second liquid to escape.

In preferred embodiments, the first and second conduits of the heat exchanger are formed of a material having a relatively high degree of heat conductivity.

In some embodiments of the invention, the inner diameter of the first conduit may be between about 0.5 and about 8 inches, between about 1 and about 6 inches, between about 1.5 and about 2 inches, between about 2 and about 3 inches, between about 3 and about 4 inches, or larger than about 8 inches.

In some embodiments of the invention, the inner diameter of the second conduit is about 25 to about 50%, about 15 to about 25%, or about 5 to about 15% of the diameter of the inner diameter of the first conduit.

In some embodiments of the invention, the pitch of the helical convolutions is about 0.2 to about 12 inches, about 1 to about 8 inches, about 3 to about 6 inches, about 2 to about 3 inches, about 1.2 to about 3.5 inches, or about 1 to about 2 inches.

In some embodiments of the invention, the first conduit has two, three, four or more helical convolutions.

In certain embodiments of the invention, the heat exchanger of the invention is adapted for use in a heat recovery device for use in a personal shower installation, wherein waste water from the shower installation passes through the first conduit, and cold water supply passes through the second conduit.

In other embodiments, the invention includes a heat recovery device adapted for use in the drain conduit of a shower installation having a hot water supply line, a cold water supply line, a means for mixing water from both said lines to deliver water at a suitable temperature to a shower head, and a drain conduit for disposing of waste water passing out of the shower installation, the heat recovery device transferring heat from the waste water to the cold water supply before the cold water supply enters said mixing means, said heat recovery device comprising the heat exchanger of the invention, wherein waste water from the shower installation passes through the first conduit, and cold water supply passes through the second conduit.

In some embodiments, a hydroforming process is used to simultaneously form the first conduit and the additional layer of material over said first conduit which forms the inner wall of the second conduit.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a general diagrammatic perspective view of a typical individual shower equipment installation incorporating one embodiment of the heat recovery device of the present invention.

FIG. 2 is an enlarged perspective view of the heat recovery device utilized in the shower equipment shown in FIG. 1.

FIG. 3 is a sectional view of the heat recovery device in FIG. 2, showing the internal structure of the device.

FIG. 4 is an enlarged detail sectional view of the end of one conduit section the heat recovery device, shown without the 90 degree end fitting in place.

FIG. 5 is a side view of a single heat exchanger subassembly of the heat recovery device of the invention, for the purpose of showing the location of sections B-B and D-D.

FIG. 6 is enlarged sectional view B-B depicting interior features.

FIG. 7 is enlarged sectional view D-D depicting interior features.

FIG. 8 is a perspective view of an embodiment of a simplified heat recovery device made from a single continuous conduit section.

FIG. 9 is a perspective view of heat exchanger made from a single tubular assembly, the horizontal section of which is formed at an angle of slightly more than 180 degrees.

FIG. 10 is an enlarged detail sectional view similar to FIG. 4, but showing an embodiment incorporating asymmetric helical features to improve mixing and heat transfer efficiency.

DETAILED DESCRIPTION OF THE INVENTION

An improved heat recovery device is disclosed which is adapted for use in the drain conduit of standard shower installations having a hot water supply line, a cold water supply line, a means for mixing water from both lines to deliver water at a suitable temperature to a shower head, and a drain conduit for disposing of waste water passing through the shower installation, the heat recovery device transferring heat from the waste water to the cold water flowing through the cold water supply line, thus reducing the amount of hot water required for a shower of a given temperature & duration. The heat recovery device consists of a three-layer structure that has a first inner conduit connected into the drain conduit of the shower installation, and an integrally formed second outer conduit connected into the cold water supply line leading to the mixing means and then to the shower head, and in intimate thermal contact with the first conduit. The integrally formed second conduit comprises of a second layer of material to provide a safe separation between the two flow streams, which generally follows the surface of the first conduit and is in close thermal contact with the first conduit. The outer wall of the second conduit is formed by a third layer, which may be a substantially straight tubular structure that is brazed or otherwise joined to the outermost surface of the second layer. The first conduit functions as a drain-trap, and is substantially unobstructed to prevent clogging, and the second conduit guides the cold water helically around the outer perimeter of the first conduit to provide the maximum possible thermal energy transfer between the conduits. The first conduit also contains said helical features in the wall that maximize the convective heat transfer from the drain water by increasing the flow velocity and turbulence of the drain water.

In one embodiment, the heat recovery device of the invention is used to preheat the incoming cold supply water, which reduces the amount of hot water required for a given shower temperature and thus reduce energy usage. It has been estimated that approximately $360 per year could be saved by the average homeowner with electric hot water with a family of four who all shower daily if the heat recovery device of this invention were utilized. The savings for gas or oil hot water would be about $120 per year. By multiplying these amounts by the number of shower installations in the United States alone, one can appreciate the significance of the economic and environmental impact of the present invention.

The novel design disclosed herein provides substantial advantages in manufacturability, material usage, operating and efficiency, which leads to critical improvements in the cost-effectiveness and thus marketability of this device.

Referring to FIG. 1, one environment in which an improved heat exchanger device of the invention may be used is shown in a general diagrammatic perspective view, indicated generally by reference numeral 10. The shower equipment 10 includes a hot water line 12 which is connected to a suitable hot water source, typically at a temperature of about 140 degrees Fahrenheit, indicated by the letter H. The downstream end of 12 is connected to the shower valve 20. The shower equipment 10 also includes an upstream cold water line 14 which is connected to a suitable cold water source, indicated by the letter C, which is not regulated in temperature but is typically 50 to 60 degrees Fahrenheit. The downstream end of the cold water line 14 is connected to the cold water input end of heat recovery device of the present invention, which is generally indicated by numeral 18 and is fully described herein below. Said cold water input of 18 is the downstream end of the heat recover device with respect to waste water flow, indicated by letter S. The cold water line also has a downstream portion 16, the downstream end of which connects to the shower valve 20, and the upstream end of which connects to the warmed water exit end of the heat recovery device of this invention, which is the upstream end of the heat recovery device 18 with respect to shower waste water flow, indicated by the letter W. The valve 20 has an exit line 22 that transports the mixture of hot and warmed supply water to the shower head indicated by the numeral 24, which is typically desired at a temperature of about 105 Fahrenheit. The purpose of the heat recovery device 18 of the present invention is to deliver the warmed cold water flow to the mixing valve 20 at the highest possible temperature, thus reducing the requirement of hot water to the least possible flow rate and saving the maximum amount of energy. As the mixed shower water W is used it flows into the drain 28 and then into the heat recover device, possibly via a short section of conduit 26, where it transfers some of its heat to the incoming cold supply water C before exiting via drain conduit 30 and traveling into a sewer or septic system. The exiting drain water S will exit the heat recovery device at a lower temperature than when it entered the device, since much of its heat has been transferred to the cold water flow stream. It should be understood that in a conventional shower equipment installation that does not have the heat recovery device in place, the adjacent ends of the upstream 26 and downstream 30 drain conduit are connected via a standard water trap, which is always filled with water in order to prevent offensive odors or dangerous gasses from traveling up through the shower drain.

Referring to FIG. 2, a perspective view of one embodiment of the heat recovery device utilized in the shower equipment shown in FIG. 1 is shown. This embodiment comprises two generally straight and parallel sections indicated by numerals 39 and 40, which are connected in series with respect to the waste water flow via two elbow fittings 37 and 38, of approximately 90 degrees each. It is appreciated that a single fitting of approximately 180 degrees can be substituted for the two 90 degree fittings, or the 180 degree turn can be integral to the straight sections. The open waste water input end 33 is comprised of an approximately 90 degree fitting 36 that transfers the flow from vertical to horizontal, and directs the flow into the first straight section of the heat exchanger. The exit opening for the waste water 34 is comprised of an approximately 90 degree fitting 35 that transfers the flow of waste water from the downstream generally horizontal straight section 40 to a generally vertical upward flow. These 90 degree entrance and exit features may also be created integrally to the straight sections if desired. This geometry comprising a generally horizontal section with generally vertical entrance and exit sections for the waste water allows the heat recovery device to always remain full of water, therefore acting as a water trap, and also increasing the efficiency of the device.

The cold water enters the heat recovery device through a fitting 32 at the end nearest the waste water exit 34, and travels through the device in the opposite direction as the waste water. A cross-over tube 41 is located at the opposite end of the straight sections with respect to the input fitting 32 and the exit fitting 31. The cross-over tube allows the cold water flow to travel from one straight section 40 to the other straight section 39. The warmed cold water flow exits the heat recovery device through fitting 31.

The path of the cold water through the heat recovery device is readily understood from the sectional perspective FIG. 3. The section is taken from a horizontal plane cut through the centerline of the straight waste water conduits, and then the section continues along the conduit centerlines until the vertical entrance and exit areas 33 & 34. As can be seen from this figure, the first conduit (i.e. the waste water conduit), indicated generally by reference numeral 1, is comprised of a tubular section, preferably made from a high thermal conductivity material, and contains a helical feature 48 in the wall of the tube. As can be seen in enlarged sectional FIG. 4, there is an additional layer of material, preferably a highly thermally conductive material indicated by numeral 47, which is integrally formed against the outer surface of conduit 1 and forms a sleeve. Said helical feature 48, when combined with the additional layer 47, and enclosed by the cylindrical outer jacket 42, forms a continuous helical second conduit 44 through which the cold water can pass and be in intimate thermal contact with the waste water. The cylindrical outer jacket 42 is formed from a highly thermally conductive material, and bonded, preferably via a brazing process, to the outermost surface 49 of the helical features 48 of the additional layer 47. The contact between the inner and outer tubular structures 47 and 42 further increases the energy transfer to the cold water flow by allowing outer jacket 42 to be heated by the waste water flow. Outer jacket 42 contains integrally formed features 43 on opposite ends that allow the entrance and exit tubes for the cold water to be attached. Said features 43 may be located on opposites sides of outer jacket 42.

The first conduit, particularly represented by 40 in FIG. 4, and the integrally formed sleeve layer 47 are not bonded to each other but are in intimate thermal contact. A hydroforming process is employed to form the structure comprising the first conduit and the sleeve part simultaneously. The inner conduit 1 is formed from a straight tube with the outer sleeve concentrically in place with a close clearance fit. The assembly is placed in a female die containing the desired outer geometry of the final assembly, and when the first conduit is expanded from the interior using a pressurized fluid against said die, the tube assembly will take the outer shape corresponding to the die shape. This process allows simultaneous forming of the first conduit 40 and sleeve 47, and guarantees that the two parts will be in close thermal contact. In one embodiment, a layer of fibrous material that can withstand the high temperatures of the brazing process is used between the two formed layers, which will create a very small air gap between the fibers and allow leaking fluid from any of the conduits to escape and thus be detected. In an alternative embodiment, sleeve part 47 is manufactured with a grooved or textured inner surface that would ensure the presence of small gaps between first conduit 40 and sleeve part 47, thus allowing water to escape from the assembly in the event that one of the inner walls starts to leak. In addition to, or in lieu of, this grooved or textured inner surface of sleeve part 47, the first conduit 40 may be manufactured with a grooved or textured outer surface to ensure the presence of said small gaps between first conduit 40 and sleeve part 47. The flow direction of cold water through fitting 34 into the second conduit is indicated by arrow 45. The flow direction of waste water out of the first conduit is indicated by arrow 46.

FIG. 5 is a side view of an individual heat exchanged tube for the present device. This view depicts the location & orientation of section B-B (FIG. 6) and D-D (FIG. 7).

FIG. 8 shows how the helical features 48 in the first conduit create the inner wall of the second conduit 44 (the sleeve layer 47 is not shown for clarity)

FIG. 9 shows an embodiment of the heat exchanger that comprises a single conduit assembly which is formed with a centrally located bend of slightly greater than 180 degrees, which simplifies the device relative to the previous embodiments by eliminating the 180 degree fittings 37 and 38 and crossover tube 41. This embodiment is more thermally efficient because the section comprising said slightly greater than 180 degree bend is part of the active heat exchange area.

FIG. 10 Is a sectional detail view of a first conduit embodiment depicting helical features which are asymmetrical. The upstream side of the helical feature 50 is much steeper than the downstream side 51, which causes rotational energy to more effectively be imparted to the waste water stream W, increasing convective heat transfer from said waste water.

The devices of the invention will advantageously be manufactured from materials of high heat conductivity. Preferably, such materials are metals. Where the heat exchanger of the present invention is to be used in a shower drain or other plumbing fixture, it will preferably made from copper, a copper alloy, or copper-plated aluminum. Notwithstanding the general preference for metals, some parts of the devices of the invention may be made from other suitable materials, even if they have a low heat conductivity. For example, one or more fittings (elbows & u-turns) or other parts may be made of plastic (e.g. PVC or ABS) although performance will be slightly better with metal fittings since these will create additional heat convection surfaces and conduction areas. In any event, the conduits should be manufactured from materials able to withstand the chemical and temperature properties of the liquids they are designed to carry. It is also contemplated that the inner surfaces of the conduits are coated (for example galvanized) with material suitably chosen to withstand the chemical and temperature properties of the liquids.

Since standard residential shower drains are between 1.5 and 2 inches in diameter, the diameter of the first conduit of the heat exchanger of the invention should preferably be between 1.5 and 2 inches. For other heat exchange applications, such as industrial process heat recovery, the diameter of the first conduit can be any suitable diameter (for example, between about 0.5 and about 8 inches, between about 1 and about 6 inches, between about 1.5 and about 2 inches, between about 2 and about 3 inches, between about 3 and about 4 inches, or larger than about 8 inches.).

Since the wall of the first conduit is convoluted, it has a variable diameter, with a minor inner diameter at its narrowest parts and a major inner diameter at its widest parts. In various embodiments, the major inner diameter is about 25 to about 50% larger, or about 15 to about 25% larger than the minor inner diameter.

The pitch of the helical convolutions of the first conduit may range from about 0.2 to about 12 inches, about 1 to about 8 inches, about 3 to about 6 inches, about 2 to about 3 inches, about 1.2 to about 3.5 inches, or about 1 to about 2 inches.

Several considerations are to be contemplated when choosing the helical pitch of the wall of the first conduit of the heat exchanger of the present invention. A lower pitch distance will result in more. “wraps” of the second conduit around the first conduit, resulting in a longer second conduit and thus a larger area for heat transfer. However, if the pitch is too small, the flow inside the first conduit will not rotate optimally, reducing the convection rate in the first conduit. Furthermore, a longer second conduit may will result in reduced pressure, which may not be desirable. On the other hand, a larger pitch will result in fewer wraps, and a shorter second conduit. This may be remedied at least in part by introducing double, triple, or more helical convolutions (i.e. creating two or more parallel flow paths in the second conduit).

EXAMPLE

A heat exchanger of the general design depicted in FIG. 8 (without the sleeve layer 47 shown in FIGS. 6 and 7) was constructed from copper. The first (inner) conduit was 92 centimeters long, formed from a single first copper tube having an inner diameter of 1.5 inches and a wall thickness of 0.080 inches. Symmetrical helical convolutions were generated by a hydroforming process wherein the first copper tube was placed in a die containing the desired geometry of the desired convolutions, and expanded from the interior using a pressurized fluid against said die. Thus, the first copper tube took the outer shape corresponding to the die shape. The inner diameter of the thus convoluted first conduit ranged from 3.8 to 5.1 centimeters, with a helical pitch of 1.25 inches. The convoluted first conduit was then inserted into a single second copper tube (corresponding to feature 42 in FIG. 8) having a wall thickness of 0.058 inches, wherein the inner diameter was equal to or slightly larger than the maximum outer diameter of the convoluted first conduit. This assembly was then braised such that the outer surface of the outermost helical portions of the first conduit were bonded to the second copper tube. This heat exchanger was then integrated into a heat recovery device in a personal shower device, with the general structure depicted in FIG. 1 (with the exception that the heat exchanger consisted of a single straight section).

The measured temperature of the hot water supply was 125 F, and the measured temperature of the cold water supply entering the heat exchanger was 42 F. The mixing valve of the personal shower device was adjusted such that the measured temperature of the water exiting the showerhead was 105 F. The measured temperature of the drain water, as it entered the drain, was 100 F. The drain (i.e. waste) water flowed at approximately 2 gallons per minute, while the cold water flow rate was 0.75 gallons per minute. The cold water and drain water flowed through the heat exchanger in opposite directions. The measured temperature of the cold water exiting the heat exchanger was 72 F (as compared to 42 F when entering the heat exchanger, see above). Thus, the calculated heat exchanger effectiveness for heating cold water was 52%.

Based on this measured temperature increase in the cold supply water from 42 F to 72 F, it was calculated that the percentage of hot water used to achieve a 105 F temperature at the shower head was reduced from 76% (without the heat recovery device) to 62% (with the heat recovery device), resulting in an 18% reduction in the volume of hot water consumed.

For the purpose of comparison to the above described working example, it was calculated that in order to achieve a heat exchanger effectiveness of approximately 50% with a conventional straight-walled (i.e. non-convoluted) design, the heat exchanger would have to be approximately 4 meters long (compare to 0.92 meter length of the device tested in the present Example. Thus, the heat exchanger device and heat recovery device of the present invention represents a very significant improvement over previously known heat exchangers suitable for this purpose, while reducing the installed size of the device in the drain area of a tub or shower, reducing the cost of the device, and greatly shortening the pay back period (amortization) of the device.

While the invention has been described in conjunction with the above working example, it will be understood that it is not intended to limit the invention to such embodiment. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims. 

1. A heat recovery device adapted for use in the drain conduit of a shower installation having a hot water supply line, a cold water supply line, a means for mixing water from both said lines to deliver water at a suitable temperature to a shower head, and a drain conduit for disposing of waste water passing out of the shower installation, the heat recovery device transferring heat from the waste water to the cold water supply before it enters said mixing means, said heat recovery device comprising: A. a section of generally tubular first conduit formed of a material having a relatively high degree of heat conductivity, said first conduit having an inlet end connected to an upstream portion of said drain conduit and an outlet end connected to a downstream portion of said drain conduit so that waste water passing through said drain conduit also passes through said first conduit, said inlet and outlet ends of said first conduit being connected to said upstream and downstream portions respectively of said drain conduit in such a manner that said first conduit between said inlet and outlet ends is disposed at a lower level than said inlet and outlet ends so that said first conduit remains filled with water at all times and functions as a water trap, and contains at least one helical convolution formed in the wall of said first conduit. B. conduit means connected into said cold water line of said shower equipment and being thermally operatively associated with said first conduit such that cold water passes through said conduit means while passing through said cold water line to be exposed to heat from said first conduit from waste water passing therethrough, said conduit means comprising a second conduit formed of a material having a relatively high degree of heat conductivity, said second conduit being disposed in intimate heat exchange relationship with said first conduit, said second conduit having an inlet end connected to an upstream portion of said cold water line and an outlet end connected to a downstream portion of said cold water line so that cold water passing through said cold water line also passed through said second conduit and receives heat transferred to said first conduit from said waste water, said second conduit having an inner wall that comprises a layer of thermally conductive material that conforms generally to the said helically convoluted outer surface of said first conduit, said second conduit having an outer wall consisting of a substantially tubular member that fits closely to the largest diameter parts of said convoluted inner wall and is suitably joined to it, so that the second conduit is comprised of the helical lumen formed between said outer and said inner walls, said outer wall containing at least one opening at each end of the helical lumen for inlet and exit flow respectively of said cold water supply suitable for adapting to common plumbing fittings, whereby heat from said waste water is conducted through said first conduit means to pre-heat cold water passing through said second conduit means before reaching said mixing means.
 2. The heat recovery device of claim 1 wherein said first conduit is substantially straight and generally horizontal, said inlet and said outlet ends are disposed at substantially 90 degrees to said first conduit means, and disposed substantially vertically.
 3. The heat recovery device of claim 2 wherein two assemblies of said first conduits and said conduit means are connected in series using a 180 degree conduit section to join them, and are arranged substantially parallel to each other in the generally horizontal plane, and said inlet end of the upstream section and the exit ends of the downstream section of the first conduit sections are disposed in a substantially vertical plane, so that they are parallel to each other and in close proximity to each other.
 4. The heat recovery device of claim 1 wherein said first conduit forms a loop in the generally horizontal plane, or at a small angle to the horizontal plane, said inlet and outlet ends disposed in relative close proximity to each other, said inlet and said outlet ends disposed at substantially 90 degrees to said first conduit means, said inlet and outlet ends disposed substantially vertically.
 5. The heat recovery device of claim 1, wherein a spacer material is located between the outer surface of the first conduit and the outer surface of the inner wall of the second conduit.
 6. The heat recovery device of claim 5, wherein the spacer material is selected from the group consisting of high temperature fibrous material, metal mesh, metal wire, glass fibers, carbon fibers, aramid fibers, and ceramic fibers.
 7. A heat exchanger for transferring heat between a first liquid and a second liquid, comprising: A. a section of generally tubular first conduit for conducting a first liquid, having at least one helical convolution formed in its wall; and B. a second conduit being thermally operatively associated with said first conduit, said second conduit being disposed in intimate heat exchange relationship with said first conduit, said second conduit having a convoluted inner wall that comprises a layer of thermally conductive material that conforms generally to the outer surface of said helically convoluted first conduit, said second conduit having an outer wall consisting of a substantially tubular member that fits closely to the largest diameter parts of said convoluted inner wall and is suitably joined to it, so that the second conduit is comprised of the helical lumen formed between said outer and said inner walls, said outer wall containing at least one opening at each end of the helical lumen for inlet and exit flow of the second liquid, respectively.
 8. The heat exchanger of claim 7, wherein a spacer material is located between the outer surface of the first conduit and the outer surface of the inner wall of the second conduit.
 9. The heat exchanger of claim 8, wherein the spacer material is selected from the group consisting of metal mesh, metal wire, glass fibers, carbon fibers, aramid fibers, and ceramic fibers.
 10. The heat exchanger of claim 7, wherein at least one of the outer surface of the first conduit and the outer surface of the inner wall of the second conduit, is grooved or textured.
 11. The heat exchanger of claim 7, wherein a space is located between the outer surface of the wall of the first conduit and the outer surface of the inner wall of the second conduit, said space being in gaseous or liquid communication with the surrounding environment, said space providing a means for accidental leakage of the first or second liquid to escape.
 12. The heat exchanger of claim 7, wherein first and second conduits are formed of a material having a relatively high degree of heat conductivity.
 13. The heat exchanger of claim 7, wherein the inner diameter of the first conduit is between about 0.5 and about 8 inches, between about 1 and about 6 inches, between about 1.5 and about 2 inches, between about 2 and about 3 inches, between about 3 and about 4 inches, or larger than about 8 inches.
 14. The heat exchanger of claim 7, wherein the inner diameter of the second conduit is about 25 to about 50%, about 15 to about 25%, or about 5 to about 15% of the diameter of the inner diameter of the first conduit.
 15. The heat exchanger of claim 7, wherein the pitch of the helical convolutions is about 0.2 to about 12 inches, about 1 to about 8 inches, about 3 to about 6 inches, about 2 to about 3 inches, about 1.2 to about 3.5 inches, or about 1 to about 2 inches.
 16. The heat exchanger of claim 7, wherein the first conduit has two, three, four or more helical convolutions.
 17. A heat recovery device for use in a personal shower installation, said heat recovery device comprising the heat exchanger of claim 7, wherein said first liquid corresponds to waste water passing out of the shower installation, and said second liquid corresponds to a cold water supply.
 18. A heat recovery device adapted for use in the drain conduit of a shower installation having a hot water supply line, a cold water supply line, a means for mixing water from both said lines to deliver water at a suitable temperature to a shower head, and a drain conduit for disposing of waste water passing out of the shower installation, the heat recovery device transferring heat from the waste water to the cold water supply before the cold water supply enters said mixing means, said heat recovery device comprising the heat exchanger of claim 7, wherein the first liquid corresponds to waste water passing out of the shower installation, and the second liquid corresponds to the cold water supply.
 19. The heat exchanger of claim 7 herein the helical convolutions in the wall of the first conduit impart turbulence to the first liquid.
 20. The heat exchanger of claim 7 whereby a hydroforming process is used to simultaneously form the first conduit and said inner wall of the second conduit. 